The Wizard of Oz

Wicked is built on the 1939 film rather than on Baum's novel, and the detail that proves it is the shoes. Baum wrote silver slippers; MGM made them ruby for Technicolor. Everything downstream, including this one, inherits the film's version. The story is a prequel to that film specifically: how the Wicked Witch of the West became wicked, why the Scarecrow, the Tin Man and the Lion are what they are, and what the Wizard actually is. It works as an argument only because the audience arrives already holding the 1939 film's account, which it then contradicts.

The musical adapts Gregory Maguire's 1995 novel, which retells the story of Oz from the side of the Wicked Witch of the West, and it builds to the events the 1939 film made famous: the house falling on the Witch's sister, Dorothy taking the shoes, the Witch melting. Its central image comes from the film rather than from Baum: the Witch's green skin, which Maguire's novel and the musical both keep, was created for the 1939 film. Baum never gives her that colour.